The instant invention relates to electronic test equipment and more particulary to a test fixture for use in combination with a computerized test system for testing printed circuit board assemblies.
Computerized test systems have generally been found to be highly effective for use in testing printed circuit board assemblies of various types. In this regard, it has been found that for both economic and practical reasons, computerized test systems generally provide the most effective means for testing printed circuit board assemblies, particularly when testing large quantities of identical printed circuit board assemblies, such as those manufactured in mass production operations. Most of the heretofore available computerized test systems have comprised test computers having software which enables them to be used for testing various portions of printed circuit board assemblies as well as various specific electronic components which are assembled in the printed circuit board assemblies. However, in order to electrically interconnect computerized test systems to printed circuit board assemblies, it has generally been necessary to use test fixtures which are adapted to receive specific printed circuit boards of predetermined configurations thereon and which are adapted to be received on specific test systems.
One specific type of computerized test system which has been heretofore available and widely used for testing printed circuit board assemblies is the Teradyne L200 test system manufactured by Teradyne, Inc. of Boston, Mass. It has been found that the L200 test system can be effectively utilized for testing various different types of printed circuit board assemblies, but that it requires the use of a different test fixture for interconnecting it with each different type of printed circuit board assembly. In this regard, the Teradyne L200 test system is operable in combination with a test fixture of a type which includes a plurality of substantially parallel "paddle cards" on the underside thereof, and hence it includes a plurality of zero insertion force edge cards connectors which are adapted to receive the paddle cards of a test fixture for securing the test fixture to the L200 test system. The paddle cards which are normally utilized in a fixture of this type comprise individual printed circuit boards having gold-edge fingers along the bottom edges thereof which are receivable in the edge card connectors of a test system for electrically connecting the paddle cards to the test system. A conventional test fixture of this type generally further comprises a flexible diaphragm having an open frame therein which is adapted to receive a printed circuit board assembly of specific configuration therein and means for electrically interconnecting the printed circuit board assembly to specific paddle cards of the fixture. In this connection, the diaphragm of a test fixture of this type is generally deformable for drawing a printed circuit board assembly on the fixture downwardly to electrically connect it to the printed circuit board assembly, and vacuum means is generally provided in the test system for drawing the diaphragm downwardly to electrically connect the printed circuit board assembly to the fixture. Accordingly, after a fixture of this type has been assembled on a test system, such as a Teradyne L200 test system, it is possible to test a plurality of printed circuit board assemblies of a specific type in rapid succession by individually placing the printed circuit board assemblies in the frame of the diaphragm, applying vacuum to the diaphragm to draw it downwardly so that the printed circuit board assembly is electrically connected to the fixture, and then electronically testing the printed circuit board assembly. However, since each fixture is adapted for use in combination with a specific type of printed circuit board assembly, it is necessary to utilize a different fixture each time a different type of printed circuit board assembly is tested on the test system. Further, it has been found that the procedures which are required for changing fixtures of this type can often be tedious and time consuming and that fixtures can be rather cumbersome, while nevertheless being relatively delicate and fragile.
The instant invention provides an improved test fixture which overcomes many of the disadvantages of the heretofore available test fixtures, particularly those of the above described type which have been used in combination with the Teradyne L200 test system. More specifically, the test fixture of the instant invention comprises a base which is adapted to be received on a test system and a removable test head which is adapted to receive a specific type of printed circuit board assembly thereon but which is removably receivable on the base. The base comprises a first diaphragm having a first open receiving frame therein for receiving the test head on the base, and the base is responsive to the vacuum means of a test system for deforming the first diaphragm in order to electrically interconnect the test head to the test system. The test head comprises a second diaphragm having a second open receiving frame therein for receiving a printed circuit board assembly on the fixture, the second diaphragm communicating with the vacuum means and being responsive thereto for deforming the second diaphragm for electrically connecting the printed circuit board assembly to the test head. The test fixture of the subject invention is preferably adapted for use in combination with a test system, such as the Teradyne L200 test system, and hence the base portion of the fixture preferably comprises a plurality of paddle cards which are adapted to be received in electrically connected relation on a test system. The base preferably further comprises a plurality of spring probes which are mounted on a fixed probe plate and electrically connected to the paddle cards, the spring probes being engageable with the test head portion of the fixture for electrically interconnecting the test head to the test system when vacuum is applied to the diaphragm of the base portion to move it toward the probe plate. A rubberized seal is preferably provided in the open frame in the diaphragm of the base, and a plurality of stop discs are preferably provided in the seal for preventing it from being overcompressed. The test head preferably comprises a plurality of spring probes and a fixed probe plate, and the spring probes on the test head are preferably positioned so that they are engageable with a printed circuit board assembly to electrically connect the printed circuit board assembly to the test head when vacuum is applied to the diaphragm of the test head. The test head preferably further comprises a plurality of contact heads which are electrically connected to the spring probes, and positioned so that they are engageable with the base to electrically connect the test head to the base when vacuum is applied to the base.
For use and operation of the test fixture of the instant invention, the base is assembled on a test system, and it is secured to the test system so that it is electrically connected thereto and so that the diaphragm of the base is in communication with the vacuum means of the test system. Thereafter, a test head is assembled on the base so that the diaphragm of the test head is in communication with the vacuum means of the test system, and a printed circuit board assembly is assembled in the open frame on the diaphragm of the test head. Thereafter, the vacuum means of the test system is actuated to electrically connect the test head to the base, and it is also actuated to electrically connect the printed circuit board assembly to the test head so that the test system can carry out the necessary electrical tests on the printed circuit board assembly. As soon as the necessary tests have been completed, the vacuum means is deactuated with respect to the test head, so that the printed circuit board assembly thereon can be replaced with another printed circuit board assembly of similar configuration. In order to test a printed circuit board assembly of a different configuration on the test system, the vacuum means is also deactuated with respect to the base, the test head is removed from the base, and a new test head which is adapted to receive the new printed circuit board assembly thereon is assembled on the base. Thereafter, the new printed circuit board assembly is positioned in the open frame of the new test head, and the vacuum means of the test system is actuated to electrically interconnect the new printed circuit board assembly to the test system so that the necessary electrical tests can be carried out. Accordingly, because the test fixture of the instant invention is a two-piece fixture which includes a base and a test head, it is only necessary to change the test head rather than the entire test fixture in order to test a different type of printed circuit board assembly on the test system. In this regard, since the test head is adapted to be quickly and easily electrically connected to the test system by applying vacuum to the base, different test heads can be quickly and easily interchanged on the base. On the other hand, the base, which requires substantially more complicated manipulations to electrically connect it to the test system, does not need to be changed each time a new type of printed circuit board assembly is tested on the test system.
Accordingly, it is an object of the instant invention to provide a test fixture for testing a printed circuit board assembly on a computerized test system wherein the test fixture includes an interchangeable test head to enable the test fixture to be adapted to accommodate different types of printed circuit board assemblies.
Another object of the instant invention is to provide a test fixture for testing a printed circuit board assembly on a computerized test system, wherein the test fixture includes a base and a test head which is removable from the base.
Other objects, features and advantages of the invention shall become apparent as the description thereof proceeds when considered in connection with the accompanying illustrative drawings.